I just got an e-mail asking what to do if you find that the blocks oil feed passage holes don,t line up exactly right with the holes in the oil feed holes in bearings shells?well different manufacturers have different bearings and you may want to find a different brand or part number bearing before you go modifying any component or the block,but I generally use CLEVITE (H) series bearings and I usually find and off set is minimal. Ive rarely seen the oil feed passages off by more than 1/16" but Ive heard of them being off by 1/8" with some bearing sets, and know that with some other engines than the BBC, SBC, and PONTIAC engines I generally build they can be much further off.since blocks are cast and the machining is done indexed off the crank center line the oil passage locations tend to be very slightly different in each block casting.the option youll generally have is to either open up the passage in the block to match the bearing shell which is generally the route most guys will take if the off set is minimal by running a counter sink bit into the opening in the oil feed passage or by using a dremel, or die grinder tool with a burr to elongate the opening on only one side to match the bearings oil feed hole.you generally won,t do much to the bearing shell itself other than in some limited cases opening the oil feed hole slightly if its in the lower groove in an upper main cap bearing as bearings are fairly easy to distort.if you are forced to make minor changes Id suggest blocking the oil feed passage with a bit of paraffin wax then carefully cleaning after wards with a rifle bore brush, high pressure air and solvent, paraffin wax has the advantage of melting into a harmless liquid that will mix with oil if a small amounts left UN-intentionally in an oil passage